In the packerhead system of concrete pipe manufacture a packerhead which consists of a rollerhead, or roller assembly, and a trowel, more frequently referred to as a longbottom, are lowered into a circular mold and rotated as they move upwardly, all the while packing wet concrete, which is dropped onto the packerhead, against the inner wall surface of the mold. Although well functioning machines are available which produce good quality pipe, both wire reinforced and non-reinforced, as epitomized by the machine disclosed in U.S. Pat. No. 4,540,539 and further improvements thereon as represented by U.S. Pat. No. 5,080,571, market dynamics require that pipe quality be further improved.
In this connection it is necessary to appreciate that industry engineering and quality standards are continually increasing, particularly with respect to reinforced pipe. As has been well known for many years, when the wire cage which constitutes the reinforcement in a concrete pipe is twisted or otherwise prevented from making a good bond with the concrete, undesirable voids form which will cause the pipe to fail post production D-load testing, which simulates fill soil loading on the pipe, and water pressure testing, or, if the tests are passed, to fail prematurely in the field. The underdesireable voids form due to twisting of the wire cage in the manufacturing process, the twisting resulting from the pressures of the rollerhead and troweling surfaces against the wet concrete, said pressures, when unbalanced, eventually exerting a twisting force on the wire cage. The cage twist phenomena can be substantially reduced by the system disclosed in U.S. Pat. No. 4,549,539 but the relationship of the speed ratios between the rollerhead and the longbottom cannot be controlled precisely enough in current machines to totally eliminate cage twist. More importantly, current systems, due to the lack of precise control of the aforesaid speed relationships, are not well suited to automatic control which, it is now known, produces the most economical and consistently high quality pipe since operator judgment, and possible misjudgment, is eliminated. Further improvements dictated by market pressures include increased production rates, component life increase, and capital investment decrease by increasing the number of sizes of pipes that can be made on a single machine.